Electric vehicle thermal management system

ABSTRACT

A method for managing thermal loads within an electric vehicle using an efficient thermal management system ( 100 ) that utilizes a single heat exchanger ( 133 ) is provided. A refrigeration subsystem ( 103 ) cools the heat exchanger ( 133 ). A first coolant loop ( 139 ) in thermal communication with the heat exchanger ( 133 ) is used to cool the energy storage system ( 137 ). A second coolant loop ( 151 ) corresponding to the HVAC subsystem ( 107 ) is also in thermal communication with the heat exchanger ( 133 ). Preferably a third coolant loop ( 109 ) corresponding to the drive motor cooling subsystem ( 101 ) is coupleable to the HVAC coolant loop ( 151 ), thus providing an efficient means of providing heat to the HVAC subsystem ( 107 ).

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/786,108, filed Apr. 11, 2007, now U.S. Pat. No. 7,789,176 thedisclosure of which is incorporated herein by reference for any and allpurposes.

FIELD OF THE INVENTION

The present invention relates generally to electric vehicles and, moreparticularly, to a method and apparatus for efficiently managing thethermal loads in an electric vehicle.

BACKGROUND OF THE INVENTION

An extremely large percentage of the world's vehicles run on gasolineusing an internal combustion engine. The use of such vehicles, morespecifically the use of vehicles which rely on fossil fuels, i.e.,gasoline, creates two problems. First, due to the finite size andlimited regional availability of such fuels, major price fluctuationsand a generally upward pricing trend in the cost of gasoline are common,both of which can have a dramatic impact at the consumer level. Second,fossil fuel combustion is one of the primary sources of carbon dioxide,a greenhouse gas, and thus one of the leading contributors to globalwarming. Accordingly, considerable effort has been spent on findingalternative drive systems for use in both personal and commercialvehicles.

Electric vehicles offer one of the most promising alternatives tovehicles that use internal combustion drive trains. One of the principalissues involved in designing an efficient electric drive train as wellas a vehicle that is “user friendly” is thermal management, primarilydue to the required operating conditions of the battery cells and theneed to provide on-demand heating and cooling within the passengercabin. To date, electric vehicle thermal management systems have hadlimited capabilities, been overly complex, or both. For example, earlygeneration electric vehicles often used multiple independent heatmanagement subsystems. Such an approach is inherently inefficient aseach heat management subsystem requires its own components (e.g., pumps,valves, refrigerant systems, etc.).

To overcome some of the problems associated with the use of independentthermal subsystems, U.S. Pat. No. 6,360,835 and related U.S. Pat. No.6,394,207 disclose a thermal management system utilizing multiple heattransfer circuits which share the same heat transfer medium. The heattransfer circuits are in fluid communication with one another, thusallowing hot heat transfer medium to flow from the high temperaturecircuit into the low temperature circuit, and cooler heat transfermedium to flow from the low temperature circuit into the hightemperature circuit. Although this system appears to overcome some ofthe limitations of the prior systems, it is still relatively complex dueto the interaction of the two heat transfer circuits.

Accordingly, what is needed in the art is a simplified thermalmanagement system that meets the power train and HVAC systemrequirements of an electric vehicle. The present invention provides sucha system.

SUMMARY OF THE INVENTION

The present invention provides a method of managing thermal loads withinan electric vehicle, the method comprising the steps of cooling a heatexchanger with a refrigeration system, circulating a first coolantwithin a first coolant loop coupled to the heat exchanger and thevehicle's energy storage system, circulating a second coolant within asecond coolant loop coupled to the heat exchanger and the vehicle's HVACsubsystem, and circulating a third coolant within a third coolant loopcoupled to the vehicle's drive motor. The method may further comprisethe step passing air through a radiator coupled to the second coolantloop, where the air passing through the radiator flows into the vehiclepassenger cabin. The method may further comprise the steps of couplingthe second coolant loop to the third coolant loop and passing airthrough a radiator coupled to the second coolant loop, where the airpassing through the radiator flows into the vehicle passenger cabin. Themethod may further comprise the steps of controlling the flow rate ofthe first and second coolants, for example using valves or circulationpumps.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a thermal management system inaccordance with the invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

FIG. 1 schematically illustrates a thermal management system 100 inaccordance with a preferred embodiment of the invention. System 100 iscomprised of four subsystems; power train cooling subsystem 101,refrigeration subsystem 103, battery cooling subsystem 105, and heating,ventilation and cooling (HVAC) subsystem 107. Each subsystem will now bedescribed in detail.

Subsystem 101 is comprised of a continuous power train cooling loop 109which is used to cool drive motor 111, the vehicle's principal tractionmotor. Preferably cooling loop 109 is also used to cool various systemelectronic components 113 (e.g., the power electronics module for motor109). System electronics 113 are preferably mounted to a cold plate 115which is used to transfer the heat away from the electronics and intothe liquid coolant (i.e., the heat transfer medium) contained in thecooling loop. Cooling loop 109 also includes a pump 117 to circulate thecoolant through the cooling loop, a radiator 119 for discharging theheat to the ambient atmosphere, and a coolant reservoir 121. Preferablythe system also includes a fan 123 for forcing air through radiator 119when insufficient air is passing through the radiator to achieve thedesired level of cooling, for example when the vehicle is not moving.

Refrigeration subsystem 103 is comprised of a compressor 125, condenser127, fan 129, thermostatic expansion valve 131, heat exchanger 133 anddryer/separator 135. Compressor 125 compresses the low temperaturerefrigerant vapor in the subsystem into a high temperature vapor. Therefrigerant vapor then dissipates a portion of the captured heat when itpasses through condenser 127, thereby leading to a phase change fromvapor to liquid, the liquid remaining at a high temperature andpressure. Preferably the performance of condenser 127 is enhanced byusing a blower fan 129. The liquid phase refrigerant then passes throughthermal expansion valve 131 which lowers both the temperature andpressure of the refrigerant as well as controlling the flow rate ofrefrigerant into heat exchanger 133. Heat exchanger 133 provides asimple means for transferring heat between the refrigerant contained insubsystem 103 and the coolants contained in the other subsystems. Afterbeing heated in heat exchanger 133, the refrigerant is separated intothe liquid and vapor phases by dryer/separator 135, thus insuring thatonly vapor passes through compressor 125. It should be appreciated thatalthough refrigeration subsystem 103 is preferred, the invention canutilize other refrigeration subsystems as long as the utilizedrefrigeration subsystem includes a heat exchanger which can be usedcooperatively with the other thermal subsystems of the vehicle asdescribed herein.

Battery cooling subsystem 105 includes the energy storage system 137(ESS) coupled to a coolant loop 139 containing the coolant (i.e., a heattransfer medium). In a typical electric vehicle, ESS 137 is comprised ofa plurality of batteries. The coolant is pumped through ESS 137,typically via a heat transfer plate (not shown) coupled to ESS 137, bycirculation pump 141. During normal operation, the coolant contained inloop 139 is cooled via heat transfer with the refrigerant in heatexchanger 133. Additionally, in a preferred embodiment of the invention,cooling loop 109 is also thermally coupled to a heater 143 (e.g., a PTCheater), thus insuring that the temperature of ESS 137 can be maintainedwithin its preferred operating range regardless of the ambienttemperature. Subsystem 105 also includes a coolant reservoir 145.

Heating, ventilation and cooling (HVAC) subsystem 107 providestemperature control for the vehicle's passenger cabin. It includes a fan147 which is used to circulate air throughout the cabin on demand,regardless of whether the air is heated, cooled, or simply fresh airfrom outside the vehicle. To provide cool air, circulating pump 149circulates coolant contained within coolant loop 151 through radiator153, the coolant contained in loop 151 being cooled by heat transferwith the refrigerant in heat exchanger 133. To provide warm air duringnormal vehicle operation, subsystem 107 is coupled to subsystem 101 viaflow control valves 155, 157, and 159, thus allowing the coolant heatedby subsystem 101 to flow through radiator 153. Additionally, in apreferred embodiment of the invention, a heater 161 (e.g., a PTC heater)is integrated within radiator 153, thus allowing cabin heating prior tothat achievable by subsystem 101 alone.

It will be appreciated that there are numerous ways of controlling theamount of cooling supplied by refrigeration subsystem 103 to the othersubsystems. One approach is through the use of valves, for example avalve within coolant loop 139 can be used to control the flow of coolantthrough the battery cooling subsystem 105 and thus the level of coolingachieved via heat exchanger 133. Similarly a valve within coolant loop151 can be used to control the flow of coolant through HVAC subsystem107 and thus the level of cooling achieved via heat exchanger 133.Alternately, as both the battery cooling subsystem 105 and the HVACsubsystem 107 place a thermal load on heat exchanger 133 ofrefrigeration subsystem 103, by simply varying the speed of the twocoolant circulation pumps within these two subsystems, i.e., coolantpumps 141 and 149, respectively, the level of cooling achieved by thetwo subsystems is continuously variable, thereby avoiding the necessityof valves within the coolant loops.

As will be understood by those familiar with the art, the presentinvention may be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof. Accordingly, thedisclosures and descriptions herein are intended to be illustrative, butnot limiting, of the scope of the invention which is set forth in thefollowing claims.

1. A method of managing thermal loads within an electric vehicle, themethod comprising the steps of: cooling a first portion of a heatexchanger with a refrigeration system, wherein said step of cooling saidfirst portion of said heat exchanger further comprises the steps ofcirculating a refrigerant within said refrigeration system and passingsaid refrigerant through a condenser and a thermal expansion valve;circulating a first coolant within a first coolant loop, wherein saidfirst coolant loop is separate from said refrigeration system and saidfirst coolant is separate from said refrigerant, wherein a first portionof said first coolant loop passes through a second portion of said heatexchanger and wherein a second portion of said first coolant loop isthermally coupled to an energy storage system, wherein said energystorage system is comprised of a plurality of batteries; circulating asecond coolant within a second coolant loop, wherein said second coolantloop is separate from said refrigeration system and said first coolantloop, wherein said second coolant is separate from said refrigerant,wherein a first portion of said second coolant loop passes through athird portion of said heat exchanger and wherein a second portion ofsaid second coolant loop is thermally coupled to a vehicle passengercabin HVAC subsystem corresponding to a vehicle passenger cabin; andcirculating a third coolant within a third coolant loop, wherein saidthird coolant loop is separate from said refrigeration system and firstcoolant loop, wherein said third coolant is separate from saidrefrigerant, and wherein said third coolant loop is thermally coupled toa vehicle drive motor.
 2. The method of claim 1, wherein said firstcoolant circulating step further comprises the step of controlling theflow rate of said first coolant through said first coolant loop, andwherein said second coolant circulating step further comprises the stepof controlling the flow rate of said second coolant through said secondcoolant loop.
 3. The method of claim 2, wherein said step of controllingthe flow rate of said first coolant is performed with a first valvewithin said first coolant loop, and wherein said step of controlling theflow rate of said second coolant is performed with a second valve withinsaid second coolant loop.
 4. The method of claim 2, wherein said firstcoolant circulating step and said first coolant flow rate controllingstep are performed with a first circulation pump within said firstcoolant loop, and wherein said second coolant circulating step and saidsecond coolant flow rate controlling step are performed with a secondcirculation pump within said second coolant loop.
 5. The method of claim1, further comprising the steps of coupling said second coolant loop tosaid third coolant loop such that said second coolant and said thirdcoolant intermix.
 6. The method of claim 5, further comprising the stepof controlling flow between said second coolant loop and said thirdcoolant loop.
 7. The method of claim 1, further comprising the step ofcirculating said third coolant through a radiator.
 8. The method ofclaim 7, further comprising the step of passing air through saidradiator using a blower fan.
 9. The method of claim 1, furthercomprising the step of thermally coupling said third coolant loop to apower electronics module.
 10. The method of claim 1, further comprisingthe step of passing air through a radiator coupled to said secondcoolant loop, wherein said air is cooled as it passes through saidradiator, and wherein said cooled air flows into said vehicle passengercabin after passing through said radiator.
 11. The method of claim 1,further comprising the step of thermally coupling said first coolantloop to a heater.
 12. The method of claim 1, further comprising the stepof thermally coupling said second coolant loop to a heater.